Warning
I see many people proposing solutions for other platforms (such as Windows or macOS). I cannot verify the authenticity of those methods, and you should not copy, paste, and run code from random people on the internet without first understanding what it does. Ideally, review every line carefully and, even then, run it with caution in a sandboxed environment.
I personally experienced slowdowns and issues while using the ja-netfilter agent.
I decided to investigate how JetBrains checks license validity, because despite explicitly configuring JetBrains to work offline, it still attempts to validate licenses.
Here are my findings: